Heparinless cardiopulmonary bypass revisited: a newer strategy to avoid heparin-related bleeding using dermatan sulfate

Oral administration of dermatan sulphate reduces venous thrombus formation in vivo: potential use as a formulation for venous thromboembolism

Dermatan sulphate (DS) is a sulphated polysaccharide that displays complexity in constituent sulphated disaccharides and interacts with proteins and signalling molecules to modulate numerous biological processes, including inhibition of the coagulation cascade and regulation of blood clotting and fibrinolysis. This study shows the antithrombotic and anticoagulant effects of DS prepared from bovine collagen waste liquor following oral and intravenous administrations in a deep vein thrombosis (DVT) rabbit model. In vitro, the prothrombin time, activated partial thromboplastin time, and thrombin citrated plasma clotting assays revealed that bovine DS had strong antithrombotic and anticoagulant effects comparable to low-molecular-weight heparin [Clexane^® (enoxaparin sodium)]. In a DVT rabbit model, animals received intravenous and oral administrations of bovine DS and Clexane^® providing further evidence that both agents had strong antithrombotic and anticoagulant effects by significantly reducing or preventing clot formation. Thromboelastography (TEG) assays revealed further that both bovine DS and Clexane^® substantially prolonged the clotting time of recalcified citrated whole blood, but only bovine DS could retain clot strength suggesting that bovine DS had less effect on platelet-fibrin interactions. In conclusion, this is the first report that oral administration of DS from bovine collagen waste liquor reduces experimental venous thrombus formation warranting further research into bovine DS as an oral antithrombotic therapeutic.

Heparin-Induced Thrombocytopenia

Heparin's anticoagulation effect makes it the principal component in the immediate treatment of all thrombotic diseases. After hemorrhage, the most important complication of heparin is thrombocytopenia, the decrease in the number of blood platelets. Ten cases of "heparin-induced thrombocytopenia" are described, and guidelines for diagnosing heparin-induced thrombocytopenia in patients who present for cardiac and vascular surgery are given. Methods of treating patients with heparin-induced thrombocytopenia, including use of arachidonic acid derivatives, antiplatelet agents, other anticoagulants, heparinoids, natural and synthetic thrombin inhibitors, hirudin, and defibrinogenation with ancrod, are discussed.

Factor V Leiden and perioperative risk

Factor V Leiden (FVL) is the most common known inherited cause of thrombophilia; it is present in approximately 5% of the Caucasian population. Although the risk of venous thrombosis associated with this polymorphism in various medical settings is well described, its effect on perioperative risk is only beginning to be explored. Specifically, there are few studies addressing the potential risks of FVL in the surgical population, in which both hemorrhagic and thrombotic complications convey substantial clinical and economic significance. There are speculations and unproven hypotheses regarding FVL in this population, and these therefore highlight the need to comprehensively address this issue. This review will describe the physiology of the FVL mutation, briefly clarify its risk in the nonsurgical setting, and assess current data regarding FVL in noncardiac and cardiac surgery. Finally, a summary of current clinical evidence and a plan for more detailed investigation of this potentially significant risk factor will be proposed.

Use of plasma exchange and heparin during cardiopulmonary bypass for a patient with heparin induced thrombocytopenia: a case report

Patients with documented history of heparin-induced thrombocytopenia (HIT) pose a difficult problem during surgery using cardiopulmonary bypass (CPB). Several alternatives to heparin exist, but these products either are not approved for use in the United States or have more side effects than heparin. We report on a patient with documented heparin-induced antibody and left main coronary artery disease who underwent uneventful coronary artery bypass surgery and recovery by using preoperative plasmaphresis and limited use of porcine intestinal heparin during CPB.

Mechanisms and attenuation of hemostatic activation during extracorporeal circulation

Patients undergoing cardiac surgery with cardiopulmonary bypass are at risk for excessive microvascular bleeding, which often leads to transfusion of allogeneic blood and blood components as well as reexploration in a smaller subset of patients. Excessive bleeding after cardiac surgery is generally related to a combination of several alterations in the hemostatic system pertaining to hemodilution, excessive activation of the hemostatic system, and potentially the use of newer, longer-acting antiplatelet or antithrombotic agents. Although several nonpharmacologic strategies have been proposed, this review summarizes the role of pharmacologic interventions as means to attenuate the alterations in the hemostatic system during CPB in an attempt to reduce excessive bleeding, transfusion, and reexploration. Specifically, agents that inhibit platelets, fibrinolysis, factor Xa and thrombin, as well as broad-spectrum agents, have been investigated with respect to their role in reducing consumption of clotting factors and better preservation of platelet function. Prophylactic administration of agents with antifibrinolytic, anticoagulant, and possibly antiinflammatory properties can decrease blood loss and transfusion. Although aprotinin seems to be the most effective blood conservation agent (which is most likely related to its broad-spectrum nature), agents with isolated antifibrinolytic properties may be as effective in low-risk patients. The ability to reduce blood product transfusions and to decrease operative times and reexploration rates favorably affects patient outcomes, availability of blood products, and overall health care costs.

Cardiopulmonary bypass in patients with heparin-induced thrombocytopenia and thrombosis

Heparin-induced thrombocytopenia and thrombosis (HITT) is an immunomediated disorder induced by the administration of heparin for therapeutic purposes. The presence of this condition in patients requiring full heparinization for cardiopulmonary bypass constitutes a formidable challenge for the cardiac surgeon. In this review, the clinical and experimental experience described in the literature are discussed in the perspective of the normal coagulation and the pathophysiology of HITT and in the light of a variety of old and new alternative anticoagulants.

Anticoagulant and antithrombin effects of intimatan, a heparin cofactor II agonist

Surface-bound thrombin, which is resistant to inhibition by heparin/antithrombin III (/AT), plays a key role in vessel wall disease. In contrast, surface-bound thrombin is not resistant to inhibition by heparin cofactor II (HCII) and its acceleration of its inhibitory effect by dermatan sulfate. However, the potential use of dermatan sulfate to prevent thrombus formation in vivo is limited by its low specific activity, which in turn, necessitates excessively high doses when given on a gravimetric basis. Recently, a novel HCII agonist, Intimatan, has been synthesized by site-specific sulphation of highly purified dermatan sulfate comprising primarily of L-iduronic acid-4-O-sulphated N-acetyl-D-galactosamine, yielding a 4, 6-O-disulphate compound on the galactopyranose ring with a lower molecular weight, higher solubility, and specific activity than its parent, dermatan sulfate. In this study, we compared the abilities of Intimatan with its parent compound, dermatan sulfate, and with heparin to affect coagulation and to inhibit surface-bound thrombin both in vitro and in vivo, to determine if Intimatan demonstrates a better potential than either other compound in preventing thrombus formation in vivo. Intimatan prolonged the activated partial thromboplastin time (APTT) more effectively than either dermatan sulfate or heparin at comparable antithrombin concentrations. This activity was attributed to the more selective action of Intimatan against surface-bound thrombin in vitro. Intimatan also inhibited thrombin bound to an injured vessel wall surface in vivo more effectively than heparin, i.e., when measured in injured carotid arteries of rabbits injected with Intimatan or with heparin at the time of injury. We conclude that Intimatan effectively inhibits surface-bound thrombin, thereby exhibiting better anticoagulant and antithrombin properties than heparin and dermatan sulfate.

Inhibition of chronic vessel wall intimal hyperplasia following acute anticoagulant treatment: relative effects of heparin and dermatan sulphate

Surface-bound thrombin which contributes to vessel wall hyperplasia, is resistant to inhibition by heparin/antithrombin III (/ATIII) but not to inhibition by dermatan sulphate/heparin cofactor II (/HCII). To determine the effects of heparin and dermatan sulphate on vessel wall hyperplasia after a first or second injury, rabbit carotid arteries first were injured, using a standard procedure (first injury). Half of the first-injury rabbits were given heparin, dermatan sulphate, or saline, 5 minutes before and at 30-minute intervals over 2 hours post-injury, and then allowed to recover. Four weeks later, the first-injury treated animals were killed and their injured carotid arteries were processed histologically. The remaining untreated first-injury rabbits were also allowed to recover. At 4 weeks, those rabbits were re-anesthetized and their first-injury arteries (which were occluded >75%), were isolated, and vessel wall lumen patency was re-established by endarterectomy (second injury). During this second injury, the animals were treated with heparin, dermatan sulphate, or saline as described above. Four weeks after this second injury, these rabbits were killed and their second injury arteries were processed histologically. Intimal hyperplasia determined histologically, was expressed as an x-fold increase in vessel wall cross-sectional area (i.e., [(media+intima area) media area]). Vessel wall lumen occlusion was expressed as [1-(lumen area/internal elastic lamina area) x 100; % occlusion]. Vessel wall area in the saline-treated animals, increased 2.6+/-1.2 and 2.4+/-1.0 fold respectively, means+/-SD, n = 12, within 4 weeks of the first and second injuries. These increases were due to intimal hyperplasia and associated with 75+/-19% and 79+/-21% occlusion of the vessel wall lumen, respectively. Heparin had little effect, whereas dermatan sulphate (1) decreased hyperplasia by 45% after the first injury and by 47% after the second injury, p<0.008 and <0.03, respectively, and (2) decreased vessel wall occlusion 47+/-12% and 33+/-5% after the first and second injury, respectively. We conclude that (1) dermatan sulphate/HCII may be a useful inhibitor of vessel wall hyperplasia following vessel wall injury, and (2) this effect can be achieved by an acute anticoagulant treatment at the time of injury, unlike heparin/ATIII.

Heparinless cardiopulmonary bypass with active-site blocked factor IXa: a preliminary study on the dog

OBJECTIVE

Cardiopulmonary bypass is a potent stimulus for activation of procoagulant pathways. Heparin, the traditional antithrombotic agent, however, is often associated with increased perioperative blood loss because of its multiple sites of action in the coagulation cascade and its antiplatelet and profibrinolytic effects. Furthermore, heparin-mediated immunologic reactions (that is, heparin-induced thrombocytopenia) may contraindicate its use. Cardiopulmonary bypass with a selective factor IXa inhibitor was tested to see whether it could effectively limit bypass circuit/intravascular space thrombosis while decreasing extravascular bleeding, thereby providing an alternative anticoagulant strategy when heparin may not be safely administered.

METHODS

Active site-blocked factor IXa, a competitive inhibitor of the assembly of factor IXa into the factor X activation complex, was prepared by modification of the enzyme's active site by the use of dansyl glutamic acid-glycine-arginine-chlormethylketone. Twenty mongrel dogs (five were given standard heparin/protamine; 15 were given activated site-blocked factor IXa doses ranging from 300 to 600 microg/kg) underwent 1 hour of hypothermic cardiopulmonary bypass, and blood loss was monitored for 3 hours after the procedure.

RESULTS

Use of activated site-blocked factor IXa as an anticoagulant in cardiopulmonary bypass limited fibrin deposition within the extracorporeal circuit as assessed by scanning electron microscopy, comparable with the antithrombotic effect seen with heparin. In contrast to heparin, effective antithrombotic doses of activated site-blocked factor IXa significantly diminished blood loss in the thoracic cavity and in an abdominal incisional bleeding model.

CONCLUSION

These initial studies on the dog suggest that administration of activated site-blocked factor IXa may be an effective alternative anticoagulant strategy in cardiopulmonary bypass when heparin is contraindicated, affording inhibition of intravascular/extracorporeal circuit thrombosis with enhanced hemostasis in the surgical wound.